Industrial water purification and desalination

ABSTRACT

This invention relates to the field of water purification and desalination. In particular, embodiments of the invention relate to systems and methods of removing essentially all of a broad spectrum of impurities from water in an automated industrial process that requires minimal cleaning or maintenance during the course of several months to several years, with relatively high yields of product water per unit of input water, flexibility with respect to energy sources, compact design with a low industrial foot-print, the ability to recover valuable by-products, and ultra-low energy requirements.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/532,766, filed Sep. 9, 2011, and the entire disclosure of thatapplication is incorporated herein by reference.

BACKGROUND

Water purification technology is rapidly becoming an essential aspect ofmodern life as conventional water resources become increasingly scarce,municipal distribution systems for potable water deteriorate with age,and increased water usage depletes wells and reservoirs, causing salinewater contamination. Additionally, further contamination of watersources is occurring from a variety of activities, which include, forexample, intensive agriculture, gasoline additives, and heavy toxicmetals. These issues are leading to increasing and objectionable levelsof germs, bacteria, salts, MTBE, chlorates, perchlorates, arsenic,mercury, and even the chemicals used to disinfect potable water, in thewater system.

Furthermore, even though almost three fourths of the earth is covered byoceans, only some 3% of this water exists as fresh water resources, andthese resources are becoming increasingly scarce as a result ofpopulation growth and global warming. Approximately 69% of all freshwater is contained in ice caps and glaciers; with increased globalmelting, this fresh water becomes unrecoverable, so less than 1% isactually available, with the majority (over 90%) being ground water inaquifers that are being progressively contaminated by human activitiesand saline incursions. Thus, there is an urgent need for technology thatcan turn saline water, including seawater and brine, into fresh water,while removing a broad range of contaminants.

Conventional desalination and water treatment technologies, includingreverse osmosis (RO) filtration and thermal distillation systems, suchas multiple-effect distillation (MED), multiple-stage flash distillation(MSF), and vapor compression distillation (VC), are rarely able tohandle the diverse range of water contaminants found in salineenvironments. Additionally, even though they are commercially available,they often require multiple treatment stages or some combination ofvarious technologies to achieve acceptable water quality. RO systemssuffer from the requirement of high-water pressures as the salinecontent increases, rendering them expensive in commercial desalination,and they commonly waste more than 40% of the incoming feed water, makingthem progressively less attractive when water is scarce. Moreover, ROinstallations produce copious volumes of waste brine that are typicallydiscarded into the sea, resulting in high saline concentrations that aredeadly to fish and shellfish. Less conventional technologies, such asultraviolet (UV) light irradiation or ozone treatment, can be effectiveagainst viruses and bacteria but seldom remove other contaminants, suchas dissolved gases, salts, hydrocarbons, and insoluble solids.Additionally, while most distillation technologies may be superior atremoving a subset of contaminants, they rarely can handle all types ofcontaminants.

Because commercial desalination plants are normally complex engineeringprojects that require one to three years of construction, they aretypically capital intensive and difficult to move from one place toanother. Their complexity and reliance on multiple technologies alsomake them prone to high maintenance costs. Because RO plants aredesigned to operate continuously under steady pressure and flowconditions, large pressure fluctuations or power interruptions candamage the membranes, which are expensive to replace; the incoming feedwater therefore requires extensive pre-treatment to prevent fouling ofthe RO membrane.

Thermal distillation systems, such as those described by LeGolf et al.(U.S. Pat. No. 6,635,150 B1) include MED systems, which rely on multipleevaporation and condensation steps that operate under vacuum in order toeffect evaporation at temperatures lower than the normal boiling pointof water. Such technologies are commercially used for desalination invarious countries, but they all operate according to differentphysico-chemical principles. For example, MED, MSF, and VC systems allrequire vacuum, which means that the product water cannot be sterilizedbecause evaporation occurs at temperatures lower than those needed forsterilization; also, vacuum systems tend to leak and require mechanicalreinforcement. In addition, heat transfer and heat recovery in MED, MSF,and VC systems involve heat exchange across membranes or thin metalsurfaces, but heat exchangers are prone to fouling and scale formationand require frequent maintenance.

More recently, Thiers (PCT Application No.: US2009/57277, entitled LargeScale Water Purification and Desalination, filed Sep. 17, 2009, and PCTApplication No.: US2010/030759, entitled Method and System for Reductionof Scaling in Purification of Aqueous Solutions, filed Apr. 12, 2010)has described a method of pre-treatment that removes scale-formingconstituents from a water stream and large scale embodiments for adesalination system. However, the earlier pre-treatment system describedby Thiers relies on a final thermal treatment that involves heating to120° C. for several minutes of residence time, which, while technicallyeffective, represents a significant energy consumption. There is a needfor a pre-treatment method that minimizes energy consumption while stillremoving scale-forming constituents from an aqueous stream. In addition,the embodiments described by Thiers for a large-scale desalination andwater treatment fail to address transient phenomena encountered duringstart-up and shut down operations and do not properly ensure themaintenance of a stable hydraulic head between different boiling stages.There is a need for industrial configurations that are stable duringstart-up and shut down procedures, in addition to being stable duringnormal operation.

There is a need for inexpensive and effective pre-treatment methods thateliminate scale-forming compounds. There is a further need forindustrial desalination and water treatment systems that are continuousand largely self-cleaning, that resist corrosion and scaling, that aremodular and compact, that recover a major fraction of the input waterwhile producing a highly concentrated waste brine that crystallizes intoa solid salt cake, and that are relatively inexpensive andlow-maintenance.

SUMMARY

The present invention describes various industrial embodiments for animproved desalination and water purification system. The system includesa pre-treatment section that prevents scale formation and a desalinationsection that consists of an inlet, a preheater, a degasser, multipleevaporation chambers and demisters, product condensers, a waste outlet,a product outlet, multiple heat pipes for heat transfer and recovery,and a control system. The control system permits operation of thepurification system continuously with minimal user intervention orcleaning. The system is capable of removing, from a contaminated watersample, a plurality of contaminant types including microbiologicalcontaminants, radiological contaminants, metals, salts, volatileorganics, and non-volatile organics. In embodiments of the system anddepending on the salinity of the incoming water stream, the volume ofwater produced can range from about 20% to in excess of 95% of a volumeof input water. The system comprises a vertical stack arrangement ofboiling chambers, condensers, and a preheater that is compact andportable. The system is capable of water production in the range of1,000 to 50 million gallons per day.

The pre-treatment section precipitates scale-forming compounds by meansof pH adjustment. Addition of either caustic or lime initiallyprecipitates magnesium hydroxide, which is subsequently removed byfiltration or sedimentation, or both. Next, the concentration ofbicarbonate ions is adjusted by dissolving CO₂ or adding bicarbonate orsoluble carbonate salts to correspond to the stoichiometric compositionof the remaining calcium, magnesium, and other divalent cations insolution, and the pH is again adjusted to values of 9.8 and higher inorder to precipitate scale-forming compounds as insoluble carbonates.Following filtration or sedimentation to remove precipitates, the clearpre-treated solution then flows into the desalination section.

The desalination section consists of a vertical stack of boilers,condensers, and demisters with a preheating tank, a degasser, and a heattransfer vessel. The preheating vessel raises the temperature of theincoming water to near the boiling point and can be placed on the top orat the bottom of the vertical stack. Water exiting the preheating tankcan have a temperature of at least about 96° C. The preheating tank mayhave a spiral arrangement of vanes such that incoming water circulatesseveral turns in the tank, thus providing sufficient residence time toeffect preheating. Incoming feed water enters the preheating tanktangentially, is gradually preheated by heat pipes until the requiredtemperature is achieved, and exits the preheating tank through adowncomer tube that connects either with the degasser or directly with alower boiling chamber if there is no need for degassing.

A degasser, which is placed near the top of the vertical stack, removesgases and organic contaminants that may be volatile or non-volatile bymeans of counter-current stripping of the incoming water againstlow-pressure steam. The degasser can be in a substantially verticalorientation, having an upper end and a lower end. Pre-heated waterenters the degasser at its upper end, and degassed water exits thedegasser proximate to the lower end. In the system, steam from thehighest evaporation chamber can enter the degasser proximate to thelower end and can exit the degasser proximate to the upper end. Thedegasser can include a matrix adapted to facilitate mixing of water andsteam, stripping the inlet water of essentially all organics, volatiles,and gases by counterflowing the inlet water against an oppositedirectional flow of a gas in a degasser. The gas can be, for example,steam, air, nitrogen, and the like. The matrix can include substantiallyspherical particles. However, the matrix can also include non-sphericalparticles. The matrix can include particles having a size selected topermit uniform packing within the degasser. The matrix can also includeparticles of distinct sizes, and the particles can be arranged in thedegasser in a size gradient. Water can exit the degasser substantiallyfree of organics and volatile gases.

The heat-transfer vessel provides the heat energy for the entire systemand can consist of a condenser chamber operating with low-pressure wastesteam. Alternatively, it can be a combustion chamber that operates withany type of fuel or a vessel that absorbs heat from a working fluid fromrecuperators, solar heaters, or economizers.

Pre-treated water is first preheated to near the boiling point andenters a degas ser proximate the upper end of the vertical stack, wheregases and hydrocarbons are removed. The degassed water then enters anupper boiler, where a portion of the incoming water is turned intosteam; a portion of the steam produced in the upper boiler may be usedto provide the required steam for degassing, while the balance enters ademister that removes entrained micro-droplets and is condensed intopure water in a condenser chamber immediately above the boiler. As someof the incoming water in the upper boiler evaporates, the balance of thewater becomes progressively more concentrated in soluble salts andcontinuously cascades downward into a series of lower boilers until itexits the lowermost boiler as a heavy brine at near the solubility limitof the salt solution.

Concurrent with incoming water cascading downward, heat is provided atthe heat-transfer vessel and is progressively transferred upwards bymeans of heat pipes. Heat pipes are highly efficient enthalpy transferdevices that operate with a small temperature difference between theirhot and cold ends. A number of heat pipes transfer the heat provided atthe heat-transfer vessel to the bottom boiler. The steam produced at thebottom boiler is largely recovered as the heat of condensation in thebottom condenser, where another set of heat pipes transfers that heat toan upper boiler, thus progressively re-using the heat for multipleevaporation and condensation chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flowsheet of the pre-treatment process.

FIG. 2 is a schematic view of a desalinator with two stages.

FIG. 3 is a detailed elevation view of a desalinator stage.

FIG. 4 is a diagram of a desalinator with five stages.

FIG. 5 provides elevation, stereoscopic, and plant views of the boiler,the condenser, and the separator plate.

FIG. 6 is a schematic diagram of a heat pipe.

FIG. 7 is a schematic view of a high-performance heat pipe.

DETAILED DESCRIPTION

Embodiments of the invention are disclosed herein, in some cases inexemplary form or by reference to one or more Figures. However, any suchdisclosure of a particular embodiment is exemplary only and is notindicative of the full scope of the invention.

Embodiments of the invention include systems, methods, and apparatusesfor water purification and desalination. Preferred embodiments providebroad spectrum water purification that is fully automated and canoperate over very long periods of time without requiring cleaning oruser intervention. For example, systems disclosed herein can run withoutuser control or intervention for 2, 4, 6, 8, 10, or 12 months, orlonger. In preferred embodiments, the systems can run automatically for1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 years, or more.

Embodiments of the invention thus provide a water purification anddesalination system including at least an inlet for saline water,contaminated water, or seawater, a preheater, a degasser, one or moreevaporation chambers, one or more demisters, and one or more productcondensers with a product outlet, a waste outlet, and a control system,wherein product water exiting the outlet is substantially pure, andwherein the control system permits operation of the purification systemcontinuously without requiring user intervention. In preferredembodiments, the volume of product water produced is at least about 20,25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98,or 99%, or more, of the volume of input water. Thus, the system is ofgreat benefit in conditions in which there is relatively high expense orinconvenience associated with obtaining inlet water and/or disposing ofwastewater. The system is significantly more efficient in terms of itsproduction of product water per unit of input water or wastewater thanmany other systems.

Substantially pure water can be, in different embodiments, water thatmeets any of the following criteria: water purified to a purity, withrespect to any contaminant, that is at least 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, 95, 100, 125, 150, 175, 200, 250, 500, 750,1000, or more, times greater in purity than the inlet water. In otherembodiments, substantially pure water is water that is purified to oneof the foregoing levels, with respect to a plurality of contaminantspresent in the inlet water. That is, in these embodiments, water purityor quality is a function of the concentration of an array of one or morecontaminants, and substantially pure water is water that has, forexample, a 25-fold or greater ratio between the concentration of thesecontaminants in the inlet water as compared to the concentration of thesame contaminants in the product water.

In other embodiments, water purity can be measured by conductivity,where ultrapure water has a conductivity typically less than about 1μSiemens, and distilled water typically has a conductivity of about 5.In such embodiments, conductivity of the product water is generallybetween about 1 and 7, typically between about 2 and 6, preferablybetween about 2 and 5, 2 and 4, or 2 and 3. Conductivity is a measure oftotal dissolved solids (TDS) and is a good indicator of water puritywith respect to salts, ions, minerals, and the like.

Alternatively, water purity can be measured by various standards, suchas, for example, current U.S. Environmental Protection Agency (EPA)standards as listed in Table 1 and Table 2, as well as other acceptedstandards as listed in Table 2. Accordingly, preferred embodiments ofthe invention are capable of reducing any of one or more contaminantsfrom a broad range of contaminants, including, for example, anycontaminant(s) listed in Table 1, wherein the final product water has alevel for such contaminant(s) at or below the level specified in thecolumn labeled “MCL” (maximum concentration level), where the inletwater has a level for such contaminant(s) that is up to about 25-foldgreater than the specified MCL. Likewise, in some embodiments and forsome contaminants, systems of the invention can remove contaminants toMCL levels when the inlet water has a contamination that is 30-, 40-,50-, 60-, 70-, 80-, 90-, 100-, 150-, 250-, 500-, or 1000-fold, or more,higher than the MCL or the product water.

While the capacity of any system to remove contaminants from inlet wateris to some extent a function of the total impurity levels in the inletwater, systems of the invention are particularly well suited to remove aplurality of different contaminants, of widely different types, from asingle feed stream, producing water that is comparable to distilledwater and is in some cases comparable to ultrapure water. It should benoted that the “Challenge Water” column in Table 1 containsconcentration levels for contaminants in water used in EPA tests.Preferred embodiments of water purification systems of the inventiontypically can remove much greater amounts of initial contaminants thanthe amounts listed in this column. However, contaminant levelscorresponding to those mentioned in the “Challenge Water” column arelikewise well within the scope of the capabilities of embodiments of theinvention.

TABLE 1 Water Contaminant Concentration Levels and Testing ProtocolsChallenge Units Protocol MCL Water 1. Metals Aluminum ppm 0.2 0.6Antimony ppm 0.006 0.1 Arsenic ppm 0.01 0.1 Beryllium ppm 0.004 0.1Boron ppb 20 Chromium ppm 0.1 0.1 Coppcr ppm 1.3 1.3 Iron ppm 0.3 8 Leadppm 0.015 0.1 Manganese ppm 0.05 1 Mercury ppm 0.002 0.1 Molybdenum ppm0.01 Nickel ppm 0.02 Silver ppm 0.1 0.2 Thallium ppm 0.002 0.01 Vanadiumppm 0.1 Zinc ppm 5 5 Subtotal of entire mix 36.84 2. Inorganic SaltsBromide ppm 0.5 Chloride ppm 250 350 Cyanide ppm 0.2 0.4 Fluoride ppm 48 Nitrate, as NO₃ ppm 10 90 Nitrite, as N₂ ppm 1 2 Sulfate ppm 250 350Subtotal of entire mix 800.9 3. 2 Highly Volatile VOCs + 2 Non-Volatiles Heptachlor ppm EPA525.2 0.0004 0.04 Tetrachloroethylene-PCEppm EPA524.2 0.00006 0.02 Epichlorohydrin ppm 0.07 0.2 Pentachlorophenolppm EPA515.4 0.001 0.1 Subtotal of cntirc mix 0.36 4. 2 Highly VolatileVOCs + 2 Non- Volatiles Carbon tctrachloridc ppm EPA524.2 0.005 0.01m,p-Xylenes ppm EPA524.2 10 20 Di(2-ethylhexyl) adipate ppm EPA525.2 0.40.8 Trichloroacetic acid ppm SM6251B 0.06 0.12 Subtotal of entire mix20.93 5. 3 Highly Volatile VOCs + 3 Non- Volatiles 1,1-Dichloroethyleneppm 0.007 0.15 Ethylbenzene ppm EPA524.2 0.7 1.5 Aldrin ppm EPA505 0.0050.1 Dalapon (2,2-dichloropropionic acid) ppm EPA515.4 0.2 0.4 Carbofuran(furadan) ppm EPA531.2 0.04 0.1 Fcnoprop (2,4,5-TP, Silvcx) ppm EPA515.40.05 0.1 Subtotal of entire mix 2.35 6. 3 Highly Volatile VOCs + 3 Non-Volatiles Trichloroethylene-TCE ppm EPA524.2 0.005 0.1 Toluene ppmEPA524.2 1 2 1,2,4-Trichlorobenzene ppm EPA524.2 0.07 0.15 2,4-D(2,4-dichlorophenoxyacetic acid) ppm EPA515.4 0.07 0.15 Alachlor(Alanex) ppm EPA525.2 0.002 0.1 Simazine ppm EPA525.2 0.004 0.1 Subtotalof entire mix 2.6 7. 3 Highly Volatile VOCs + 3 Non- VolatilesVinylchloride (chloroethene) ppm EPA524.2 0.002 0.1 1,2-Dichlorobenzene(1,2-DCB) ppm EPA524.2 0.6 1 Chlorobcnzcnc ppm EPA524.2 0.1 0.2 Atrazineppm EPA525.2 0.003 0.1 Endothal ppm EPA548.1 0.01 0.2 Oxamyl (Vydate)ppm EPA531.2 0.2 0.4 Subtotal of entire mix 2.0 8. 3 Highly VolatileVOCs + 3 Non- Volatiles Styrene ppm EPA524.2 0.1 1 Benzene ppm EPA524.20.005 0.2 Methoxychlor ppm EPA525.2/505 0.04 0.1 Glyphosate ppm EPA5470.7 1.5 Pichloram ppm EPA515.4 0.5 1 1,3-Dichlorobenzene (1,3-DCB) ppmEPA524.2 0.075 0.15 Subtotal of entire mix 3.95 9. 3 Highly VolatileVOCs + 3 Non- Volatiles 1,2-Dichloropropane (DCP) ppm EPA524.2 0.005 0.1Chloroform ppm EPA524.2 80 0.1 Bromomethane (methyl bromide) ppmEPA524.2 0.1 PCB 1242 (Aroclor 1242) ppb EPA505 0.5 1 Chlordane ppmEPA525.2/505 0.002 0.2 MEK (methylehtylketone, 2-butanone) ppb EPA524.20.2 Subtotal of entire mix 1.7 10. Group: 4 VOCs + 5 Non-Volatile PCBs2,4-DDE (dichlorodiphcnyl dichloroethylene) ppm EPA525.2 0.1Bromodichloromethane ppb EPA524.2 80 0.1 1,1,1-Trichloroethane (TCA) ppmEPA524.2 0.2 0.4 Bromoform ppm EPA524.2 80 0.1 PCB 1221 (Aroclor 1221)ppm EPA505 0.5 0.05 PCB 1260 (Aroclor 1260) ppm EPA505 0.5 0.05 PCB 1232(Aroclor 1232) ppm EPA505 0.5 0.05 PCB 1254 (Aroclor 1254) ppm EPA5050.5 0.05 PCB 1016 (Aroclor 1016) ppm EPA505 0.5 0.05 Subtotal of entiremix 0.95 11. 5 VOCs + 5 Non-Volatile PCBs Dichloromethane (DCM,methylene ppm EPA524.2 0.005 0.1 chloride) 1,2-Dichloroethane ppm 0.0050.1 Lindane (gamma-BHC) ppm EPA525.2 0.0002 0.05 Benzo[a]pyrene ppmEPA525.2 0.0002 0.05 Endrin ppm EPA525.2/505 0.002 0.051,1,2-Trichloroethane (TCA) ppm EPA524.2 0.005 0.05 MTBE (methyl t-butylether) ppm EPA524.2 0.05 Ethylene dibromide (EDB) ppm EPA504.1 0.000050.05 Dinoseb ppm EPA515.4 0.007 0.05 Bis(2-ethylhexyl) phthalate (DEHP)ppm EPA525.2 0.006 0.05 Subtotal of entire mix 0.6 12. 6 VOCsChloromethane (methyl chloride) ppm EPA524.2 0.1 Toxaphene ppm EPA5050.003 0.1 trans-1,2-Dichloroethylene ppm EPA524.2 0.1 0.2Dibromochloromethane ppm EPA524.2 80 0.05 cis-1,2-Dichloroethylene ppmEPA524.2 0.07 0.05 1,2-Dibromo-3-chloro propane ppm EPA504.1 0.0002 0.05Subtotal of entire mix 0.55

Determination of water purity and/or efficiency of purificationperformance can be based upon the ability of a system to remove a broadrange of contaminants. For many biological contaminants, the objectiveis to remove substantially all live contaminants. Table 2 listsadditional common contaminants of source water and standard protocolsfor testing levels of these contaminants. The protocols listed in Tables1 and 2 are publicly available at www.epa.gov/safewater/mcl.html#mclsfor common water contaminants, as well as Methods for the Determinationof Organic Compounds in Drinking Water, EPA/600/4-88-039, December 1988,revised July 1991. Methods 547, 550, and 550.1 are in Methods for theDetermination of Organic Compounds in Drinking Water—Supplement I,EPA/600-4-90-020, July 1990. Methods 548.1, 549.1, 552.1, and 555 are inMethods for the Determination of Organic Compounds in DrinkingWater—Supplement II, EPA/600/R-92-129, August 1992. Methods 502.2,504.1, 505, 506, 507, 508, 508.1, 515.2, 524.2 525.2, 531.1, 551.1, and552.2 are in Methods for the Determination of Organic Compounds inDrinking Water—Supplement III, EPA/600/R-95-131, August 1995. Method1613 is titled “Tetra-through Octa-Chlorinated Dioxins and zFurans byIsotope Dilution HRGC/HRMS,” EPA/821-B-94-005, October 1994. Each of theforegoing is incorporated herein by reference in its entirety.

TABLE 2 Water Contaminant Testing Protocols Protocol 1 Metals andInorganics Asbestos EPA100.2 Free cyanide SM 4500CN-F Metals - Al, Sb,Be, B, Fe, Mn, Mo, Ni, Ag, Tl, V, EPA200.7/200.8 Zn Anions - NO₃—N,NO₂—N, Cl, SO₄, EPA300.0A total nitrates/nitrites Bromide EPA300.0/300.1Turbidity EPA180.1 2 Organics Volatile organics - VOASDWA list +nitrozbenzene EPA524.2 EDB and DBCP EPA504.1 Semivolatile organics -ML525 list + EPTC EPA525.2 Pesticides and PCBs EPA505 Hcrbicidcs -rcgulatcd/unrcgulatcd compounds EPA515.4 Carbamates EPA531.2 GlyphosateEPA547 Diquat EPA549.2 Dioxin EPA1613b 1,4-Dioxane EPA8270m NDMA - 2 pptMRL EPA1625 3 Radiologicals Gross alpha and beta EPA900.0 Radium 226EPA903.1 Uranium EPA200.8 4 Disinfection By-Products THMs/HANs/HKsEPA551.1 HAAs EPA6251B Aldehydes SM 6252m Chloral hydrate EPA551.1Chloramines SM 4500 Cyanogen chloride EPA524.2m

TABLE 3 Exemplary Contaminants for System Verification MCLG¹ 1 Metals &Inorganics Asbcstos <7 MFL² Free cyanide <0.2 ppm Mctals - Al, Sb, Bc,B, Fe, Mn, Mo, Ni, Ag, Tl, V, 0.0005 ppm Zn Anions - NO₃—N, NO₂—N, Cl,SO₄, <1 ppm total nitrates/nitrites Turbidity <0.3 NTU 2 OrganicsVolatile organics - VOASDWA list + nitrobenzene EDB and DBCP 0 ppmSemivolatile organics - ML525 list + EPTC <0.001 ppm Pesticides and PCBs<0.2 ppb Herbicides - regulated/unregulated compounds <0.007 ppmGlyphosate <0.7 ppm Diquat <0.02 ppm Dioxin 0 ppm 3 Radiologicals Grossalpha and bcta <5 pCi/l³ Radium 226 0 pCi/l³ Uranium <3 ppb 4Disinfection By-Products Chloramines 4 ppm Cyanogen chloride 0.1 ppm 5Biologicals Cryptosporidium 0⁴ Giardia lamblia 0⁴ Total coliforms 0⁴¹MCLG = maximum concentration limit guidance ²MFL = million fibers perliter ³pCi/l = pico Curies per liter ⁴Substantially no detectablebiological contaminants

Overall Description of Water Pre-Treatment System

The objective of the pre-treatment system is to reduce scale-formingcompounds to a level at which they will not interfere by forming scalein subsequent treatment, particularly during desalination. Waterhardness is normally defined as the amount of calcium (Ca⁺⁺), magnesium(Mg⁺⁺), and other divalent ions that are present in the water and isnormally expressed in parts per million (ppm) of these ions or theirequivalent as calcium carbonate (CaCO₃). Scale forms because the waterdissolves carbon dioxide from the atmosphere, and such carbon dioxideprovides carbonate ions that combine to form both calcium and magnesiumcarbonates; upon heating, the solubility of calcium and magnesiumcarbonates markedly decreases, and they precipitate as scale. Inreality, scale comprises any chemical compound that precipitates fromsolution. Thus, iron phosphates and calcium sulfate (gypsum) alsoproduce scale. Table 4 lists a number of chemical compounds that exhibitlow solubility in water and can thus form scale. In this context, lowsolubility is defined by the solubility product, that is, by the productof the ionic concentration of cations and anions of a particularchemical; solubility is usually expressed in moles per liter (mol/L).

TABLE 4 Solubility Products of Various Compounds Compound Formula K_(sp)(25° C.) Aluminum hydroxide Al(OH)₃   3 × 10⁻³⁴ Aluminum phosphate AlPO₄9.84 × 10⁻²¹ Barium bromatc Ba(BrO₃)₂ 2.43 × 10⁻⁴  Barium carbonateBaCO₃ 2.58 × 10⁻⁹  Barium chromate BaCrO₄ 1.17 × 10⁻¹⁰ Barium fluorideBaF₂ 1.84 × 10⁻⁷  Barium hydroxide octahydrate Ba(OH)₂ × 8H₂O 2.55 ×10⁻⁴  Barium iodate Ba(IO₃)₂ 4.01 × 10⁻⁹  Barium iodate monohydrateBa(IO₃)₂ × H₂O 1.67 × 10⁻⁹  Barium molybdate BaMoO₄ 3.54 × 10⁻⁸  Bariumnitrate Ba(NO₃)₂ 4.64 × 10⁻³  Barium selenate BaSeO₄ 3.40 × 10⁻⁸  Bariumsulfate BaSO₄ 1.08 × 10⁻¹⁰ Barium sulfite BaSO₃  5.0 × 10⁻¹⁰ Beiylliumhydroxide Be(OH)₂ 6.92 × 10⁻²² Bismuth arsenate BiAsO₄ 4.43 × 10⁻¹⁰Bismuth iodide BiI 7.71 × 10⁻¹⁹ Cadmium arsenate Cd₃(AsO₄)₂  2.2 × 10⁻³³Cadmium carbonate CdCO₃  1.0 × 10⁻¹² Cadmium fluoride CdF₂ 6.44 × 10⁻³ Cadmium hydroxide Cd(OH)₂  7.2 × 10⁻¹⁵ Cadmium iodate Cd(IO₃)₂  2.5 ×10⁻⁸ Cadmium oxalate trihydrate CdC₂O₄ × 3H₂O 1.42 × 10⁻⁸  Cadmiumphosphate Cd₃(PO₄)₂ 2.53 × 10⁻³³ Cadmium sulfide CdS   1 × 10⁻²⁷ Cesiumperchlorate CsClO₄ 3.95 × 10⁻³  Cesium periodate CsIO₄ 5.16 × 10⁻⁶ Calcium carbonate (calcite) CaCO₃ 3.36 × 10⁻⁹  Calcium carbonate(aragonite) CaCO₃  6.0 × 10⁻⁹ Calcium fluoride CaF₂ 3.45 × 10⁻¹¹ Calciumhydroxide Ca(OH)₂ 5.02 × 10⁻⁶  Calcium iodate Ca(IO₃)₂ 6.47 × 10⁻⁶ Calcium iodatc hcxahydratc Ca(IO₃)₂ × 6H₂O 7.10 × 10⁻⁷  Calciummolybdate CaMoO 1.46 × 10⁻⁸  Calcium oxalate monohydrate CaC₂O₄ × H₂O2.32 × 10⁻⁹  Calcium phosphate Ca₃(PO₄)₂ 2.07 × 10⁻³³ Calcium sulfateCaSO₄ 4.93 × 10⁻⁵  Calcium sulfate dihydrate CaSO₄ × 2H₂O 3.14 × 10⁻⁵ Calcium sulfate hemihydrate CaSO₄ × 0.5H₂O  3.1 × 10⁻⁷ Cobalt(II)arsenate Co₃(AsO₄)₂ 6.80 × 10⁻²⁹ Cobalt(II) carbonate CoCO₃  1.0 × 10⁻¹⁰Cobalt(II) hydroxide (blue) Co(OH)₂ 5.92 × 10⁻¹⁵ Cobalt(II) iodatedihydrate Co(IO₃)₂ × 2H₂O 1.21 × 10⁻²  Cobalt(II) phosphate Co₃(PO₄)₂2.05 × 10⁻³⁵ Cobalt(II) sulfide (alpha) CoS   5 × 10⁻²² Cobalt(II)sulfide (beta) CoS   3 × 10⁻²⁶ Copper(I) bromide CuBr 6.27 × 10⁻⁹ Copper(I) chloride CuCl 1.72 × 10⁻⁷  Copper(I) cyanide CuCN 3.47 × 10⁻²⁰Copper(I) hydroxide Cu₂O   2 × 10⁻¹⁵ Copper(I) iodide CuI 1.27 × 10⁻¹²Copper(I) thiocyanate CuSCN 1.77 × 10⁻¹³ Copper(II) arsenate Cu₃(AsO₄)₂7.95 × 10⁻³⁶ Copper(II) hydroxide Cu(OH)₂  4.8 × 10⁻²⁰ Copper(II) iodatemonohydrate Cu(IO₃)₂ × H₂O 6.94 × 10⁻⁸  Copper(II) oxalate CuC₂O₄ 4.43 ×10⁻¹⁰ Copper(II) phosphate Cu₃(PO₄)₂ 1.40 × 10⁻³⁷ Copper(II) sulfide CuS  8 × 10⁻³⁷ Europium(III) hydroxide Eu(OH)₃ 9.38 × 10⁻²⁷ Gallium(III)hydroxide Ga(OH)₃ 7.28 × 10⁻³⁶ Iron(II) carbonate FeCO₃ 3.13 × 10⁻¹¹Iron(II) fluoride FeF₂ 2.36 × 10⁻⁶  Iron(II) hydroxide Fe(OH)₂ 4.87 ×10⁻¹⁷ Iron(II) sulfide FeS   8 × 10⁻¹⁹ Iron(III) hydroxide Fe(OH)₃ 2.79× 10⁻³⁹ Iron(III) phosphate dihydrate FePO₄ × 2H₂O 9.91 × 10⁻¹⁶Lanthanum iodate La(IO₃)₃ 7.50 × 10⁻¹² Lead(II) bromide PbBr₂ 6.60 ×10⁻⁶  Lead(II) carbonate PbCO₃ 7.40 × 10⁻¹⁴ Lead(II) chloride PbCl₂ 1.70× 10⁻⁵  Lead(II) chromate PbCrO₄   3 × 10⁻¹³ Lead(II) fluoride PbF₂  3.3× 10⁻⁸ Lead(II) hydroxide Pb(OH)₂ 1.43 × 10⁻²⁰ Lead(II) iodate Pb(IO₃)₂3.69 × 10⁻¹³ Lead(II) iodide PbI₂  9.8 × 10⁻⁹ Lead(II) oxalate PbC₂O₄ 8.5 × 10⁻⁹ Lead(II) selenate PbSeO₄ 1.37 × 10⁻⁷  Lead(II) sulfate PbSO₄2.53 × 10⁻⁸  Lead(II) sulfide PbS   3 × 10⁻²⁸ Lithium carbonate Li₂CO₃8.15 × 10⁻⁴  Lithium fluoride LiF 1.84 × 10⁻³  Lithium phosphate Li₃PO₄2.37 × 10⁻⁴  Magnesium ammonium phosphate MgNH₄PO₄   3 × 10⁻¹³ Magnesiumcarbonate MgCO₃ 6.82 × 10⁻⁶  Magnesium carbonate trihydrate MgCO₃ × 3H₂O2.38 × 10⁻⁶  Magnesium carbonate pentahydrate MgCO₃ × 5H₂O 3.79 × 10⁻⁶ Magnesium fluoride MgF₂ 5.16 × 10⁻¹¹ Magnesium hydroxide Mg(OH)₂ 5.61 ×10⁻¹² Magnesium oxalate dihydrate MgC₂O₄ × 2H₂O 4.83 × 10⁻⁶  Magnesiumphosphate Mg₃(PO₄)₂ 1.04 × 10⁻²⁴ Manganese(II) carbonate MnCO₃ 2.24 ×10⁻¹¹ Manganese(II) iodate Mn(IO₃)₂ 4.37 × 10⁻⁷  Manganese(II) hydroxideMn(OH)₂   2 × 10⁻¹³ Manganese(II) oxalate dihydrate MnC₂O₄ × 2H₂O 1.70 ×10⁻⁷  Manganese(II) sulfide (pink) MnS   3 × 10⁻¹¹ Manganese(II) sulfide(green) MnS   3 × 10⁻¹⁴ Mcrcury(I) bromidc Hg₂Br₂ 6.40 × 10⁻²³Mercury(I) carbonate Hg₂CO₃  3.6 × 10⁻¹⁷ Mercury(I) chloride Hg₂Cl₂ 1.43× 10⁻¹⁸ Mcrcury(I) fluoridc Hg₂F₂ 3.10 × 10⁻⁶  Mercury(I) iodide Hg₂I₂ 5.2 × 10⁻²⁹ Mercury(I) oxalate Hg₂C₂O₄ 1.75 × 10⁻¹³ Mcrcury(I) sulfatcHg₂SO₄  6.5 × 10⁻⁷ Mercury(I) thiocyanate Hg₂(SCN)₂  3.2 × 10⁻²⁰Mercury(II) bromide HgBr₂  6.2 × 10⁻²⁰ Mercury(II) hydroxide HgO  3.6 ×10⁻²⁶ Mercury(II) iodide HgI₂  2.9 × 10⁻²⁹ Mercury(II) sulfide (black)HgS   2 × 10⁻⁵³ Mercury(II) sulfide (red) HgS   2 × 10⁻⁵⁴ Neodymiumcarbonate Nd₂(CO₃)₃ 1.08 × 10⁻³³ Nickel(II) carbonate NiCO₃ 1.42 × 10⁻⁷ Nickel(II) hydroxide Ni(OH)₂ 5.48 × 10⁻¹⁶ Nickel(II) iodate Ni(IO₃)₂4.71 × 10⁻⁵  Nickel(II) phosphate Ni₃(PO₄)₂ 4.74 × 10⁻³² Nickel(II)sulfide (alpha) NiS   4 × 10⁻²⁰ Nickel(II) sulfide (beta) NiS  1.3 ×10⁻²⁵ Palladium(II) thiocyanate Pd(SCN)₂ 4.39 × 10⁻²³ Potassiumhexachloroplatinate K₂PtCl₆ 7.48 × 10⁻⁶  Potassium perchlorate KClO₄1.05 × 10⁻²  Potassium periodate KIO₄ 3.71 × 10⁻⁴  Praseodymiumhydroxide Pr(OH)₃ 3.39 × 10⁻²⁴ Radium iodate Ra(IO₃)₂ 1.16 × 10⁻⁹ Radium sulfate RaSO₄ 3.66 × 10⁻¹¹ Rubidium perchlorate RuClO₄ 3.00 ×10⁻³  Scandium fluoride ScF₃ 5.81 × 10⁻²⁴ Scandium hydroxide Sc(OH)₃2.22 × 10⁻³¹ Silver(I) acetate AgCH₃COO 1.94 × 10⁻³  Silver(I) arsenateAg₃AsO₄ 1.03 × 10⁻²² Silver(I) bromate AgBrO₃ 5.38 × 10⁻⁵  Silver(I)bromide AgBr 5.35 × 10⁻¹³ Silver(I) carbonate Ag₂CO₃ 8.46 × 10⁻¹²Silver(I) chloride AgCl 1.77 × 10⁻¹⁰ Silver(I) chromate Ag₂CrO₄ 1.12 ×10⁻¹² Silver(I) cyanide AgCN 5.97 × 10⁻¹⁷ Silver(I) iodate AgIO₃ 3.17 ×10⁻⁸  Silver(I) iodide AgI 8.52 × 10⁻¹⁷ Silver(I) oxalate Ag₂C₂O₄ 5.40 ×10⁻¹² Silver(I) phosphate Ag₃PO₄ 8.89 × 10⁻¹⁷ Silver(I) sulfate Ag₂SO₄1.20 × 10⁻⁵  Silver(I) sulfite Ag₂SO₃ 1.50 × 10⁻¹⁴ Silver(I) sulfideAg₂S   8 × 10⁻⁵¹ Silver(I) thiocyanate AgSCN 1.03 × 10⁻¹² Strontiumarsenate Sr₃(AsO₄)₂ 4.29 × 10⁻¹⁹ Strontium carbonate SrCO₃ 5.60 × 10⁻¹⁰Strontium fluoride SrF₂ 4.33 × 10⁻⁹  Strontium iodate Sr(IO₃)₂ 1.14 ×10⁻⁷  Strontium iodate monohydrate Sr(IO₃)₂ × H₂O 3.77 × 10⁻⁷  Strontiumiodate hexahydrate Sr(IO₃)₂ × 6H₂O 4.55 × 10⁻⁷  Strontium oxalate SrC₂O₄  5 × 10⁻⁸ Strontium sulfatc SrSO₄ 3.44 × 10⁻⁷  Thallium(I) bromateTlBrO₃ 1.10 × 10⁻⁴  Thallium(I) bromide TlBr 3.71 × 10⁻⁶  Thallium(I)chloride TlCl 1.86 × 10⁻⁴  Thallium(I) chromate Tl₂CrO₄ 8.67 × 10⁻¹³Thallium(I) hydroxide Tl(OH)₃ 1.68 × 10⁻⁴⁴ Thallium(I) iodate TlIO₃ 3.12× 10⁻⁶  Thallium(I) iodide TlI 5.54 × 10⁻⁸  Thallium(I) thiocyanateTlSCN 1.57 × 10⁻⁴  Thallium(I) sulfide Tl₂S   6 × 10⁻²² Tin(II)hydroxide Sn(OH)₂ 5.45 × 10⁻²⁷ Yttrium carbonate Y₂(CO₃)₃ 1.03 × 10⁻³¹Yttrium fluoride YF₃ 8.62 × 10⁻²¹ Yttrium hydroxide Y(OH)₃ 1.00 × 10⁻²²Yttrium iodate Y(IO₃)₃ 1.12 × 10⁻¹⁰ Zinc arsenate Zn₃(AsO₄)₂  2.8 ×10⁻²⁸ Zinc carbonate ZnCO₃ 1.46 × 10⁻¹⁰ Zinc carbonate monohydrate ZnCO₃× H₂O 5.42 × 10⁻¹¹ Zinc fluoride ZnF 3.04 × 10⁻²  Zinc hydroxide Zn(OH)₂  3 × 10⁻¹⁷ Zinc iodate dihydrate Zn(IO₃)₂ × 2H₂O  4.1 × 10⁻⁶ Zincoxalatc dihydratc ZnC₂O₄ × 2H₂O 1.38 × 10⁻⁹  Zinc selenide ZnSe  3.6 ×10⁻²⁶ Zinc selenite monohydrate ZnSe × H₂O 1.59 × 10⁻⁷  Zinc sulfidc(alpha) ZnS   2 × 10⁻²⁵ Zinc sulfide (beta) ZnS   3 × 10⁻²³

Conventional descaling technologies include chemical and electromagneticmethods. Chemical methods utilize either pH adjustment, chemicalsequestration with polyphosphates, zeolites and the like, or ionicexchange; combinations of these methods are typically used. Normally,chemical methods aim at preventing scale from precipitating by loweringthe pH and using chemical sequestration, but they are typically not 100%effective. Electromagnetic methods rely on the electromagneticexcitation of calcium or magnesium carbonate so as to favorcrystallographic forms that are non-adherent. For example,electromagnetic excitation favors the precipitation of aragonite ratherthan calcite; the former is a softer, less adherent form of calciumcarbonate. However, electromagnetic methods are only effective overrelatively short distances and residence times. There is a need forpermanently removing scale-forming constituents from contaminatedaqueous solutions, seawater, or produced waters that will be subject tobe further processing.

Other factors can complicate scale reduction methods, particularly inhigh-salinity solutions such as seawater or produce water. These includethe buffering effects of high ionic strength solutions and ioncomplexing phenomena that can shield certain cations from reacting.

An embodiment of the present invention provides a method for removingscale-forming compounds from tap water, contaminated aqueous solutions,seawater, and saline brines such as produced water, involving theinitial removal of magnesium ions by precipitating magnesium hydroxide(Mg(OH)₂) at high pH, then removing the precipitate by eithersedimentation or filtering. Ordinarily, Mg(OH)₂ precipitates at high pH(around 11.0), although in many cases the bulk of magnesium precipitatesat lower pH.

Following Mg(OH)₂ precipitation, carbonate ions are added in the form ofCO₂ sparging, by adding soluble carbonate or bicarbonate salts in nearlystoichiometric amounts so as to subsequently precipitate calcium,barium, and other divalent cations as carbonates by adjusting the pH toabout 10.2 or greater. This process has the net effect of permanentlysequestering CO₂ from the atmosphere, and the precipitates are thenremoved by either sedimentation or filtering.

A detailed description of this pre-treatment embodiment follows theflowsheet of FIG. 1. In FIG. 1, filtered and de-oiled contaminated water(1) enters the pretreatment system through a line-booster pump P101(20), which delivers the incoming water into a mixer-settler vesselV-101 (40). The pH of vessel V-101 is maintained at about 11 by means ofcontinuous alkali additions, in the form of sodium hydroxide, calciumhydroxide, or similar chemical. Control of the pH in vessel V-101 isachieved through a metering pump P102 (22), which transfers causticsolution from tank T101 through a variable valve Va101 (45). Theprecipitated Mg(OH)₂ slurry in vessel V101 sediments and exits near thebottom and is continuously filtered in filter F101 (50), thus yielding afilter cake (66) of magnesium hydroxide.

Following precipitation of Mg(OH)₂ in vessel V101 (40), the clearsolution exits near the top and flows into a static mixer M101 (60),where it is mixed with additional clear filtrate from filter F101 (50)and pump P103 (24) and a source of carbonate ions, which can bepressurized CO₂ gas from V102 (32) or a solution of soluble carbonatesor bicarbonates.

The aqueous solution then flows into a second static mixer M102, whereadditional caustic or alkali chemicals are added from the variable valveVa101 (45) so as to adjust the pH to about 10.2, at which point most ofthe divalent cations in solution precipitate as insoluble carbonates.The precipitate slurry then enters mixer-settler V103 (42), where theinsoluble carbonates sediment and flow into filter F102 (52), where asecond filter cake (68) is removed. The filtrate from filter F102 enterspump P105 (26), which feeds a variable valve Va102 (47) that allows aportion of the descaled water product (70) to recirculate back into thecarbonation loop.

In a further aspect, especially when the contaminated water containsexcess carbonate or bicarbonate ions, calcium or magnesium can be addedin order to provide the stoichiometric requirements for carbonateprecipitation. Alternatively, calcium and magnesium can be substitutedfor other divalent cations, such as barium, cadmium, cobalt, iron, lead,manganese, nickel, strontium, or zinc, that have low solubility productsin carbonate form.

In a further aspect, calcium or magnesium additions are substituted fortrivalent cations, such as aluminum or neodymium, that have lowsolubility products in their carbonate or hydroxide forms.

In a further aspect, CO₂ sparging is replaced by the addition of solublebicarbonate ions, such as sodium, potassium, or ammonium bicarbonate.

In a further aspect, carbonate and scale precipitates are removed bymeans other than sedimentation or filtering, such as centrifuging.

In a further aspect, the permanent sequestration of CO₂ from theatmosphere is achieved in conventional desalination systems, such as MSFevaporation systems, MED plants, and VC desalination systems.

In a further aspect, scale-forming salts are permanently removed fromconventional desalination systems.

In a further aspect, tap water, municipal water, or well watercontaining objectionable hard water constituents, such as calcium ormagnesium, are descaled in residential water purification systems.

In a further aspect, valuable scale-forming salts, such as magnesium,barium, and other salts, are recovered.

In a further aspect, scale-forming compounds are precipitated in theform of non-adhering, easily filterable or sedimentable solids andultimately removed.

In a further aspect, CO₂ emissions from power plants and similar fluegases are permanently sequestered.

In a further aspect, scale-forming compounds are sequentiallyprecipitated and removed, so they can be utilized and reused indownstream industrial processes.

A further embodiment of the present invention provides a method forremoving a scale-forming compound from an aqueous solution, involving:adding at least one ion to the solution in a stoichiometric amountsufficient to cause the precipitation of a first scale-forming compoundat an alkaline pH; adjusting the pH of the solution to an alkaline pH,thereby precipitating the first scale-forming compound; removing thefirst scale-forming compound from the solution; heating the solution toa temperature sufficient to cause the precipitation of a secondscale-forming compound from the solution; and removing the secondscale-forming compound from the solution.

In a further aspect, the ion is selected from the group includingcarbonate ions and divalent cations. In a further aspect, the carbonateion is HCO₃ ⁻. In a further aspect, the divalent cation is selected fromthe group including Ca²⁺ and Mg²⁺.

In a further aspect, the stoichiometric amount is sufficient tosubstitute the divalent cation for a divalent cation selected from thegroup including barium, cadmium, cobalt, iron, lead, manganese, nickel,strontium, and zinc in the first scale-forming compound.

In a further aspect, the stoichiometric amount is sufficient tosubstitute the divalent cation for a trivalent cation selected from thegroup including aluminum and neodymium in the first scale-formingcompound.

In a further aspect, adding at least one ion comprises sparging thesolution with CO₂ gas.

In a further aspect, the CO₂ is atmospheric CO₂.

In a further aspect, adding at least one ion comprises adding a solublebicarbonate ion selected from the group including sodium bicarbonate,potassium bicarbonate, and ammonium bicarbonate to the solution.

In a further aspect, adding at least one ion comprises adding a compoundselected from the group including CaO, Ca(OH)₂, Mg(OH)₂, and MgO to thesolution.

In a further aspect, the alkaline pH is a pH of approximately 9.2 orgreater.

In a further aspect, the first scale-forming compound is selected fromthe group including CaCO₃ and MgCO₃.

Tn a further aspect, adjusting the pH of the solution comprises adding acompound selected from the group including CaO and NaOH to the solution.

In a further aspect, removing the first scale-forming compound comprisesat least one of filtration, sedimentation, and centrifuging.

A further embodiment of the present invention provides a method ofobtaining scale-forming compounds, involving: providing an aqueoussolution; adding alkali chemicals in amounts sufficient to cause theprecipitation of a first scale-forming compound at an alkaline pH;adjusting the pH of the solution to an alkaline pH, therebyprecipitating the first scale-forming compound; removing the firstscale-forming compound from the solution; adding carbonate ions whilemaintaining an alkaline pH sufficient to cause the precipitation of asecond scale-forming compound from the solution; removing the secondscale-forming compound from the solution; recovering the firstscale-forming compound; and recovering the second scale-formingcompound.

In a further aspect, the first and second scale-forming compounds areselected from the group of compounds listed in Table 4.

A further embodiment of the present invention provides a method ofsequestering atmospheric CO₂, involving: providing an aqueous solutioncontaining at least one ion capable of forming a CO₂-sequesteringcompound in the presence of carbonate ion; adding carbonate ions to thesolution in a stoichiometric amount sufficient to cause theprecipitation of the CO₂-sequestering compound at an alkaline pH;adjusting the pH of the solution to an alkaline pH, therebyprecipitating the CO₂-sequestering compound; and removing theCO₂-sequestering compound from the solution; wherein adding carbonateions comprises adding either atmospheric or concentrated CO₂ (e.g., froma combustion flue gas) to the solution, and wherein the CO₂ issequestered in the CO₂-sequestering compound.

Overall Description of Water Desalination System

In preferred embodiments, such as those shown in FIG. 2, the waterpurification and desalination system consists of a vertically stackedarrangement of boilers (92 and 96) and condensers (90, 94, and 98),whereby a source of heat is provided at the bottom of the stack, apreheater (74) is provided at the top of the stack, a degasser (80) isprovided at the top of the system to remove volatile organic compoundsfrom the incoming water, a plurality of demisters (not shown) areprovided to remove contaminated mist particles from each boilingchamber, a plurality of heat pipes (78) is provided to recover heat fromeach condenser and transfer such heat to an upper boiling chamber, and awaste stream outlet (100) is provided to remove and drain watercontaminants. Various alternative configurations to the vertical stackedarrangement are possible to those skilled in the art, such as, forexample, a lateral arrangement of boilers, condensers, and preheaters,and the like.

In FIG. 2, pre-treated water (70) enters the desalinator proximate theupper end of the stack through a pipeline (72), which delivers the flowinto a preheater tank (74). A number of heat pipes (78) in the preheatertank (74) deliver the heat to preheat the incoming water by transferringthe heat of condensation from the condenser (90) that is placedimmediately below. The preheated water exits the preheater tank (74)through a pipe (76), which delivers the preheated water into the upperend of a degasser (80), where it flows by gravity downward while acounter current of steam flows upward from the boiler (92) through thebottom of the degasser (80). As steam strips organic contaminants andgases from the preheated water, the degassed water exits the degasser(80) and enters the boiler (92).

Preheated and degassed water that enters the boiler (92) is furtherheated by heat pipes (78) that transfer the heat of condensation from acondenser (94). The steam produced in the boiler (92) is cleaned in ademister that is described below and is condensed in a condenser (90),and the clean water product exits the system via a pipe (102), whichcollects clean water product from each condenser. As water is evaporatedfrom the boiler (92), the concentration of dissolved salts increases.The level of boiling water in the boiler (92) is maintained at aconstant level by a downcomer tube (101), which allows water to exit theboiler by gravity.

An important element in the vertical arrangement of boilers andcondensers is the ability to maintain a slight pressure differentialbetween boilers, so that a lower boiler will have a slightly higherpressure than an upper boiler; therefore, the temperature of the lowerboiler will be slightly higher than that of an upper boiler. Thispressure differential can be maintained by a pump, but, in a preferredembodiment, it is simply maintained by the hydraulic head of thedowncomer tubes (100) and (101), which maintain such pressuredifferential by means of a lower pressure-actuated valve (103).

A more detailed description of the vertical arrangement of boilers andcondensers is provided in FIG. 3. In FIG. 3, the boiler (92) receiveshot incoming water from the downcomer tube (101), which either drains anupper boiler or receives water from the degasser. In the boiler (92),the heat pipes (78) transfer the necessary heat to bring the temperatureto the boiling point and provide the heat of evaporation to transformpart of the boiling water into steam. The steam that is produced entersa demister (110), where mist particles are collected by a series ofmechanical barriers that allow only clean steam to enter a steam tube(115), which delivers such steam to an upper condenser chamber (90),where it condenses into clean water product that drains through theproduct water drain (102).

As water boils in the boiler (92), it becomes denser and moreconcentrated in soluble salts and exits through the downcomer tube (100)into a lower boiler (96). A valve (103) at the bottom of the downcomertube (100) provides the necessary hydraulic pressure to maintain thelower boiler (96) at a slightly higher pressure and, thus, at a slightlyhigher temperature than the upper boiler (92).

The tubes (120) and (130) and the intermediate valve (125) serve dualfunctions. During start-up procedures, the valve (125), which can becontrolled by a pressure regulator or a solenoid, is open, allowingsteam to travel directly from the lower boiler (96) to the upper boiler(92), thus accelerating start-up procedures. Once the system isoperating at the correct temperature, the valve (125) is closed. Duringshut-down procedures, the heat source is shut off, and the valve (125)is re-opened so as to facilitate draining of all the boilers.

FIG. 4 is a diagram of a desalinator with five vertical stages. In FIG.4, pre-treated and descaled water (70) enters through a tube (72) intoan upper preheater vessel (74), where heat from heat pipes (78) providethe necessary energy for preheating the incoming water close to itsboiling point but no less than 96° C. The preheated water exits thepreheater (74) and enters the degasser (80), where counter-current steamstrips the gases and organic contaminants. The degassed water then flowsinto an upper boiler (92), where the heat pipes provide the necessaryheat for turning a portion of the incoming water into steam. Some of thesteam produced in the upper boiler (92) may be used to provide the steamfor degassing, while the rest flows into the demister (110) andsubsequently into an upper condenser (90), where it condenses into pureproduct water. As water evaporates in the upper boiler (92), it becomesmore concentrated in soluble salts and flows by gravity into a lowerboiler via the downcomer tube (100). The boiler water becomesprogressively more concentrated in soluble salts as it travels downwardfrom boiler to boiler until it reaches the lowest boiler, where it exitsthe system as a concentrated hot brine that can begin crystallizing assoon as it cools down. In the case of desalination, the hot waste brinemay have a TDS concentration on the order of 250,000 ppm; thisconcentration is still lower than the solubility limit of NaCl but isclose enough to begin crystallization upon cooling.

In contrast with water flow, heat travels upward in the system, from theheat input vessel at the bottom (150) ultimately to the preheatingvessel at the top (74), by means of multiple stages of heat pipes (78).At each stage, the heat of condensation or, in the case of the heatinput vessel at the bottom (150), the latent heat of flue gases or theheat of condensation of waste steam, is absorbed by a series of heatpipes that transfer the heat to an upper boiler and, at the top of thevertical stack, to the upper preheating tank (74).

An important advantage of the system described herein is the mechanismof heat transfer via heat pipes. As shown in a subsequent section, heatpipes provide a means of transferring heat that is nearlythermodynamically reversible, that is, a system that transfers enthalpywith almost no losses in efficiency. Thus, with the exception of thepreheating energy, nearly all of the heat provided by the heat inputvessel at the bottom (150) is re-used at each of the boiling andcondensing stages by minimizing heat losses at the wall separating thecondensing side of the heat pipe from the boiling side. Since thatdistance is defined by the perforated plate (93), which can be very thinor made as an insulator, the amount of heat lost during heat transfercan be close to zero. Therefore, the energy used during multiple stagesof boiling and condensing can be readily approximated by dividing theheat of evaporation of water by the number of stages of the system.

However, as the number of stages in the system increases, the amount ofsteam produced at each stage decreases; with a large number of stages,the amount of heat that condenses at the upper condenser is insufficientto provide the necessary heat for preheating the incoming water and alsoinsufficient for providing the necessary steam required for degassing.Table 5 illustrates these energy requirements for the case of seawater,which is normally devoid of organic contaminants, as a function of thenumber of stages in the system, but ignoring degassing requirements.

TABLE 5 Energy Requirements, Kwh/m³ Stages Total heat 5 133.4693 6111.2245 7 95.33525 8 86.67204 10 69.98837 20 36.62103 30 25.49859 4019.93736 50 16.60063

The above estimates presume that the heat available in the hot wastebrine at the bottom of the system and the heat contained in the variousproduct water streams is recovered either by means of heat exchangers orheat pipes. In a simple arrangement, most of this heat can be recoveredby preheating the incoming water in exchange with each of the productstreams as they cascade downward in a vertical system, ending with heatrecovery from the waste brine, and then re-pumping this preheated waterto the top of the system, where a minimal amount of supplemental heat isrequired to bring the temperature up to the boiling point.

In alternative embodiments, the product water at each stage can bere-introduced into an upper condenser stage and allowed to flash, thusreleasing part of the contained heat. In other embodiments, the incomingpre-treated water can be divided into separate streams and introducedinto each separate stage for distillation.

FIG. 5 illustrates plant, stereoscopic, and elevation views of a typicalstage and provides dimensions for a boiler, condenser, and separatorplate suitable for a system able to process on the order of 100,000 gpd(378.5 m³/day) in 6 stages.

It is advantageous to be able to maximize the number of boiling andcondensing stages in the present invention. This is possible through theuse of heat pipes, provided the temperature difference between thecondensing and boiling ends of such a heat pipe (the ΔT) is sufficientto maintain the maximum heat flux through the heat pipe. Commerciallyavailable heat pipes typically have ΔTs of the order of 8° C. (15° F.),although some have ΔTs as low as 3° C. The ΔT defines the maximum numberof stages that are practical with a given amount of heat available at agiven temperature. Thus, there is a need for heat pipes that canfunction with as small a ΔT as possible. It is therefore useful toexamine the thermal phenomena in a heat pipe.

FIG. 6 illustrates a typical commercial heat pipe, which ordinarilyconsists of a partially evacuated and sealed tube (77) containing asmall amount of a working fluid (81); this fluid is typically water butmay also be an alcohol or other volatile liquid. When heat is applied tothe lower end in the form of enthalpy, the heat crosses the metalbarrier of the tube (77), then is used to provide the heat ofvaporization to the working fluid (81). As the working fluid evaporates,the resulting gas (which is steam in the case of water) fills the tube(77) and reaches the upper end, where the ΔT causes condensation andrelease of the same heat as the heat of condensation. To facilitatecontinuous operation, the inside of the tube (77) normally includes awick (79), which can be any porous and hydrophilic layer that transfersthe condensed phase of the working fluid back to the hot end of thetube.

Experimentally, the largest barriers to heat transfer in a heat pipeinclude: 1) the layer immediately adjacent to the outside of the heatpipe, 2) the conduction barrier presented by the material of the heatpipe, and 3) the limitation of the wick material to return working fluidto the hot end of the heat pipe. FIG. 7 illustrates a high-performanceheat pipe that minimizes these barriers.

In FIG. 7, vibrational energy (87) is provided to the heat pipe (78),either in the form of mechanical vibration, electro-mechanicalvibration, or high-frequency ultrasound. This vibration is transmittedto the length of the heat pipe and disrupts the layer adjacent to theheat pipe. Disruption of this layer facilitates micro-turbulence in thelayer, thus resulting in heat transfer. In addition, a hydrophobiccoating is provided on the outside of the heat pipe, especially in thearea where external condensation occurs. The hydrophobic coating mayconsist of a monolayer of stearic acid or similar hydrocarbon, or it maybe a thin layer of a hydrophobic chlorofluorocarbon. A hydrophobicsurface on the outside of the heat pipe minimizes the area required forcondensation and evaporation, thus reducing the barrier for heattransfer.

The heat conduction barrier is also minimized by using a very thin metalfoil (77) instead of the solid metal tube of most heat pipes. Mechanicalsupport for the metal foil must be sufficient to sustain moderate vacuumand is provided by a metal screen (85), which provides additionalfunctionality by increasing the internal surface area required forproviding the necessary heat of condensation/evaporation.

An improved distribution of working fluid is achieved by orienting thewick toward the axis of the heat pipe, thus reducing the thermalinterference of condensate with heat transfer across the wall of theheat pipe. The wick material can be any hydrophilic porous medium thatcan transfer working fluid by capillary action, such as metallic oxides,some ceramics, surface-treated cellulosic materials, and the like.

In some embodiments, the system for descaling water and salinesolutions, embodiments of which are disclosed herein, can be combinedwith other systems and devices to provide further beneficial features.For example, the system can be used in conjunction with any of thedevices or methods disclosed in U.S. Provisional Patent Application No.60/676,870, entitled SOLAR ALIGNMENT DEVICE, filed May 2, 2005; U.S.Provisional Patent Application No. 60/697,104, entitled VISUAL WATERFLOW INDICATOR, filed Jul. 6, 2005; U.S. Provisional Patent ApplicationNo. 60/697,106, entitled APPARATUS FOR RESTORING THE MINERAL CONTENT OFDRINKING WATER, filed Jul. 6, 2005; U.S. Provisional Patent ApplicationNo: 60/697107, entitled IMPROVED CYCLONE DEMISTER, filed Jul. 6, 2005;PCT Application No: US2004/039993, filed Dec. 1, 2004; PCT ApplicationNo: US2004/039991, filed Dec. 1, 2004; PCT Application No:US2006/040103, filed Oct. 13, 2006; U.S. patent application Ser. No.12/281,608, filed Sep. 3, 2008; PCT Application No. US2008/03744, filedMar. 21, 2008; and U.S. Provisional Patent Application No. 60/526,580,filed Dec. 2, 2003; each of the foregoing applications is herebyincorporated by reference in its entirety.

One skilled in the art will appreciate that these methods and devicesare and may be adapted to carry out the objects and obtain the ends andadvantages mentioned, as well as various other advantages and benefits.The methods, procedures, and devices described herein are presentlyrepresentative of preferred embodiments and are exemplary and are notintended as limitations on the scope of the invention. Changes thereinand other uses will occur to those skilled in the art which areencompassed within the spirit of the invention and are defined by thescope of the disclosure.

The invention illustratively described herein suitably can be practicedin the absence of any element or elements, limitation or limitationswhich is not specifically disclosed herein. The terms and expressionswhich have been employed are used as terms of description and not oflimitation, and there is no intention that the use of such terms andexpressions indicates the exclusion of equivalents of the features shownand described or portions thereof. It is recognized that variousmodifications are possible within the scope of the invention disclosed.Thus, it should be understood that although the present invention hasbeen specifically disclosed by preferred embodiments and optionalfeatures, modification and variation of the concepts herein disclosedmay be resorted to by those skilled in the art and that suchmodifications and variations are considered to be within the scope ofthis invention as defined by the disclosure.

Those skilled in the art will recognize that the aspects and embodimentsof the invention set forth herein can be practiced separately from eachother or in conjunction with each other. Therefore, combinations ofseparate embodiments are within the scope of the invention as disclosedherein.

All patents and publications are herein incorporated by reference to thesame extent as if each individual publication was specifically andindividually indicated to be incorporated by reference.

Example #1—Water Descaling System for Seawater

The approximate chemical composition of seawater is presented in Table6, below, and is typical of open ocean, but there are significantvariations in seawater composition depending on geography and/orclimate.

TABLE 6 Detailed Composition of Seawater at 3.5% Salinity Element At.Weight ppm Hydrogcn H₂O 1.00797 110,000 Oxygen O₂ 15.9994 883,000 SodiumNaCl 22.9898 10,800 Chlorine NaCl 35.453 19,400 Magnesium Mg 24.3121,290 Sulfur S 32.064 904 Potassium K 39.102 392 Calcium Ca 10.08 411Bromine Br 79.909 67.3 Helium He 4.0026 0.0000072 Lithium Li 6.939 0.170Beryllium Be 9.0133 0.0000006 Boron B 10.811 4.450 Carbon C 12.011 28.0Nitrogen ion 14.007 15.5 Fluorine F 18.998 13 Neon Ne 20.183 0.00012Aluminum Al 26.982 0.001 Silicon Si 28.086 2.9 Phosphorus P 30.974 0.088Argon Ar 39.948 0.450 Scandium Sc 44.956 <0.000004 Titanium Ti 47.900.001 Vanadium V 50.942 0.0019 Chromium Cr 51.996 0.0002 Manganese Mn54.938 0.0004 Iron Fe 55.847 0.0034 Cobalt Co 58.933 0.00039 Nickel Ni58.71 0.0066 Copper Cu 63.54 0.0009 Zinc Zn 65.37 0.005 Gallium Ga 69.720.00003 Germanium Ge 72.59 0.00006 Arsenic As 74.922 0.0026 Selenium Se78.96 0.0009 Krypton Kr 83.80 0.00021 Rubidium Rb 85.47 0.120 StrontiumSr 87.62 8.1 Yttrium Y 88.905 0.000013 Zirconium Zr 91.22 0.000026Niobium Nb 92.906 0.000015 Molybdcnum Mo 95.94 0.01 Ruthenium Ru 101.070.0000007 Rhodium Rh 102.905 . Palladium Pd 106.4 . Silver Ag 107.8700.00028 Cadmium Cd 112.4 0.00011 Indium In 114.82 . Tin Sn 118.690.00081 Antimony Sb 121.75 0.00033 Tellurium Te 127.6 . Iodine I 166.9040.064 Xenon Xe 131.30 0.000047 Cesium Cs 132.905 0.0003 Barium Ba 137.340.021 Lanthanum La 138.91 0.0000029 Cerium Ce 140.12 0.0000012Prasodymium Pr 140.907 0.00000064 Neodymium Nd 144.24 0.0000028 SamariumSm 150.35 0.00000045 Europium Eu 151.96 0.0000013 Gadolinium Gd 157.250.0000007 Terbium Tb 158.924 0.00000014 Dysprosium Dy 162.50 0.00000091Holmium Ho 164.930 0.00000022 Erbium Er 167.26 0.00000087 Thulium Tm168.934 0.00000017 Ytterbium Yb 173.04 0.00000082 Lutetium Lu 174.970.00000015 Hafnium Hf 178.49 <0.000008 Tantalum Ta 180.948 <0.0000025Tungsten W 183.85 <0.000001 Rhenium Re 186.2 0.0000084 Osmium Os 190.2 .Iridium Ir 192.2 . Platinum Pt 195.09 . Gold Au 196.967 0.000011 MercuryHg 200.59 0.00015 Thallium Tl 204.37 . Lead Pb 207.19 0.00003 Bismuth Bi208.980 0.00002 Thorium Th 232.04 0.0000004 Uranium U 238.03 0.0033Plutonium Pu (244) . Note: ppm = parts per million = mg/liter = 0.001g/kg

Fifty gallons of ocean seawater were collected and treated in a pilotfacility able to continuously handle from 20 to 200 gallons/day.Initially, 50 mL/liter of a 10% sodium hydroxide (caustic) solution wasused to raise the pH of the seawater to approximately 11.2 and theresulting precipitate allowed to sediment in a thickener prior tofiltering using a 1μ pore filter. The filtrate was then conditioned with0.9 g/liter of sodium bicarbonate, and the pH was adjusted to 10.2 so asto obtain another precipitate of carbonate salts, which was againallowed to sediment and was subsequently filtered using a micron filter.Chemical analysis of the final filtrate showed a reduction of about 67%of the scale-forming ions, such as calcium and magnesium, with thebalance of calcium and magnesium forming soluble chlorides that do notprecipitate upon boiling.

In a similar experiment, one liter of ocean seawater was treated with 30mL of a 10% sodium hydroxide (caustic) solution was used to raise the pHof the seawater to slightly less than 11.0 and the resulting precipitateallowed to sediment in a thickener prior to filtering using a 1μ porefilter. The filtrate was then conditioned with 0.9 g/liter of sodiumbicarbonate, and the pH was adjusted to 9.8 by adding another 0.7 g ofcaustic solution so as to obtain a precipitate of carbonate salts whichwas allowed to sediment and was subsequently filtered using a 1μ filter.No scale formation compounds were detected in the resulting filtrate.

A special test procedure was developed for ascertaining the degree ofdescaling in treated solutions. In this test, a sample of treatedsolution is collected in a glass beaker, and the sample is subjected toboiling in a pressure cooker for up to 5 hours at temperatures of 120°C. under pressure. Following this test procedure, the sample is removedand inspected visually as well as under a microscope to detect any solidprecipitate. Since the residence time in the desalinating section thatfollows is only a couple of hours, the absence of any scale in thisparticular test proves that no scale will form during desalination. Innone of the examples described herein was any scale detected afterpre-treatment.

Example #2—Removal of Scale in Treatment of Waste Influent Compositions

An aqueous waste influent composition obtained as a waste stream from afertilizer processing facility was treated in the manner described abovein order to remove scale-forming compounds, as a pre-treatment toeventual desalination of the product in a separate water purificationapparatus in which the formation of scale would be highly undesirable.The throughput of the treatment apparatus was 6 gallons per day (GPD),which was used a pilot apparatus for testing an industrial situationrequiring 2000 m³/day (528,401.6 GPD). The composition of the wasteinfluent with respect to relevant elements and ions is given in Table 7below.

TABLE 7 Waste Influent Composition Soluble Salts ppm (mg/L) Barium 0Calcium 500 Magnesium 300 Iron (III) 2 Bicarbonate Sulfate 800 Phosphate0 Silica 50 Strontium Sodium 700 Potassium 30 Arsenic 0 Fluoride 2Chloride 1000 Nitrate 10

The waste influent had a TDS content of 35,000 ppm (mg/L). As can beseen from Table 7, the waste influent had particularly highconcentrations of calcium and magnesium, which tend to give rise toscale.

The waste influent was processed in the manner described above. Becausethe influent contained little or no hydrocarbons, deoiling and degassingwere not conducted. CO₂ carbonation and addition of NaOH (to providehydroxide ions to react with the Mg in solution) were followed by pHadjustment to a pH of 9.3 using additional NaOH. The process resulted ina filtered scale-forming composition (“filter cake”) and an effluent(product). The effluent product was tested for scale formation accordingto the procedure described above, and no scale or precipitate wasdetected.

Example #3—Removal of Scale in Treatment of Produced Water

The treatment process of the present disclosure was applied to seawaterthat had been adjusted to a high level of TDS and a high degree of waterhardness, in order to test the capacity of the process to deal with suchinput solutions as produced water from oil extraction operations orwaste water from gas fracking operations. The water was pretreated usingthe process of the present disclosure before being purified in a waterdesalination apparatus such as that described in U.S. Pat. No.7,678,235. As discussed in greater detail below, the seawater subjectedto the pretreatment process of the present disclosure showed noformation of scale when used as feed water in the water purificationapparatus.

The following amounts of various compounds were added to fresh oceanwater to produce the input aqueous solution of the present example: 7grams/liter of Ca(OH)₂ were added to produce a target Ca^(t)′concentration of 7.1 kppm, and 29 grams/liter of NaCl were also added.The TDS of the resulting water sample was 66 kppm.

A first precipitation was conducted at room temperature by addingapproximately 5 grams/liter of NaOH as necessary to increase the pH ofthe solution to greater than 10.5. A milky precipitate containing mainlymagnesium hydroxide was precipitated in this first room temperatureprocedure. The water was filtered to remove the solid precipitates.

A second precipitation was then conducted by adding sodium bicarbonateand sufficient caustic to adjust the pH to 9.8, and a second precipitatecontaining mainly calcium and other carbonates was obtained. The TDS ofthe descaled and filtered water was approximately 65 kppm.

The descaled water was used as an influent for a water purificationapparatus in accordance with U.S. Pat. No. 7,678,235. The product waterwas collected from the apparatus, and the TDS of the product water wasmeasured. While the inlet water had a TDS of 65 kppm, the product waterof the water purification apparatus was less than 10 ppm. No appreciabledevelopment of scale was observed in the boiler of the apparatus.

Example #4—Desalination of Ocean Water

Fifty gallons of ocean water were first pre-treated according to theprocedures described earlier and fed into a pilot desalinator designedfor a 50-200 GPD throughput. The product water had a TDS of less than 10ppm, and no signs of scale formation were detected in any of theboilers.

Example #5—Desalination of Produced Water

Fifty gallons of a synthetic produced water containing in excess of146,000 ppm of TDS and significant alkalinity were first pre-treatedaccording to the procedures described earlier and fed into a pilotdesalinator designed for a 50-200 GPD throughput. The product water hada TDS of less than 40 ppm, and no signs of scale formation were detectedin any of the boilers.

Example #6—Desalination of Brackish Water

Fifty gallons of brackish water containing in excess of 3,870 ppm of TDSwere first pre-treated according to the procedures described earlier andfed into a pilot desalinator designed for a 50-200 GPD throughput. Theproduct water had a TDS of less than 10 ppm, and no signs of scaleformation were detected in any of the boilers.

What is claimed is:
 1. A water purification and desalination systemcomprising a pre-treatment section and a desalination section, whereinthe pre-treatment permanently removes scale-forming compounds whileyielding valuable by-products and CO₂ sequestration, and wherein thedesalination section permits continuous operation of the purificationand desalination without requiring user intervention or cleaning, andwherein the system is capable of removing, from a contaminated watersample, a plurality of contaminant types selected from the groupconsisting of: microbiological contaminants, radiological contaminants,metals, salts, volatile organics, and non-volatile organics, whilerecovering the energy of distillation multiple times, and wherein thesystem's energy source is selected from the group consisting of:electricity, geothermal energy, solar energy, the combustion of oil,hydrocarbons, or natural gas, or waste heat.
 2. The method of claim 1,wherein removal of scale-forming compounds from an aqueous solutioncomprises: adding at least one ion to the solution in a stoichiometricamount sufficient to cause the precipitation of a first scale-formingcompound at an alkaline pH; adjusting the pH of the solution to analkaline pH, thereby precipitating the first scale-forming compound;removing the first scale-forming compound from the solution; addinganother ion to the solution while adjusting pH to an alkaline pH tocause the precipitation of other scale-forming compounds; and removingother scale-forming compounds from the solution.
 3. The method of claim2, wherein the first ion is selected from the group consisting of sodiumhydroxide, potassium hydroxide, calcium hydroxide, and similarhydroxides.
 4. The method of claim 2, wherein the pH is adjusted tobetween 10.5 and 11.0
 5. The method of claim 2, wherein the second ionis a carbonate or bicarbonate ion.
 6. The method of claim 2, wherein thesecond ion is a divalent cation is a Ca²⁺ or Mg²⁺ ion.
 7. The method ofclaim 6, wherein the stoichiometric amount is sufficient to substitutethe divalent cation for a divalent cation selected from the groupconsisting of barium, cadmium, cobalt, iron, lead, manganese, nickel,strontium, and zinc in the first scale-forming compound.
 8. The methodof claim 6, wherein the stoichiometric amount is sufficient tosubstitute the divalent cation for a trivalent cation selected from thegroup consisting of aluminum and neodymium in the first scale-formingcompound.
 9. The method of claim 5, wherein adding a second ioncomprises sparging the solution with CO₂ gas.
 10. The method of claim 9,wherein the CO₂ is atmospheric CO₂.
 11. The method of claim 5, whereinadding a second ion comprises adding to the solution a solublebicarbonate ion selected from the group consisting of sodiumbicarbonate, potassium bicarbonate, and ammonium bicarbonate.
 12. Themethod of claim 2, wherein the second precipitation is carried out at apH of between 9.8 and 10.0.
 13. The method of claim 2, wherein removingthe first scale-forming compound comprises at least one step selectedfrom the group consisting of filtration, sedimentation, andcentrifuging.
 14. The method of claim 2, wherein the secondscale-forming compound comprises an insoluble carbonate compound. 15.The method of claim 2, wherein removing the second scale-formingcompound comprises at least one step selected from the group consistingof filtration, sedimentation, and centrifuging.
 16. The method of claim2, additionally comprising removing contaminants from the solution priorto adding at least one ion.
 17. The method of claim 16, wherein thecontaminants are selected from the group consisting of solid particlesand hydrocarbon droplets.
 18. The method of claim 16, wherein theaqueous solution is selected from the group consisting of tap water,contaminated aqueous solutions, seawater, and saline brines contaminatedwith hydrocarbons.
 19. A method of obtaining scale-forming compounds,comprising: providing an aqueous solution; carrying out the method ofclaim 2; recovering the first scale-forming compound; and recovering thesecond scale-forming compound.
 20. The method of claim 19, wherein thefirst and second scale-forming compounds are selected from the group ofcompounds listed in Table
 4. 21. A method of sequestering atmosphericCO₂, comprising: providing an aqueous solution containing at least oneion capable of forming a CO₂-sequestering compound in the presence ofcarbonate ion; adding carbonate ions to the solution in a stoichiometricamount sufficient to cause the precipitation of the CO₂-sequesteringcompound at an alkaline pH; adjusting the pH of the solution to analkaline pH, thereby precipitating the CO₂-sequestering compound; andremoving the CO₂-sequestering compound from the solution, wherein addingcarbonate ions comprises adding atmospheric CO₂ to the solution, andwherein the atmospheric CO₂ is sequestered in the CO₂-sequesteringcompound.
 22. The method of claim 21, wherein the alkaline pH is a pH ofapproximately 9.2 or greater.
 23. The method of claim 21, wherein theCO₂-sequestering compound is selected from the group consisting ofCaCO₃, BaCO₃, SrCO₃, MgCO₃, and similar carbonates.
 24. The method ofclaim 21, wherein removing the CO₂-sequestering compound comprises atleast one step selected from the group consisting of filtration,sedimentation, and centrifuging.
 25. An apparatus for removing ascale-forming compound from an aqueous solution, comprising: an inletfor the aqueous solution; a source of caustic solution for pHadjustment, selected from the group consisting of NaOH, KOH, Ca(OH)₂,and similar hydroxides; a first tank in fluid communication with theinlet and the caustic solution; a filter in fluid communication withsaid first tank, wherein said filter is adapted to separate a firstscale-forming compound from the solution in said first tank; a source ofCO₂ gas; a source of a pH-raising agent, which can be in fluidcommunication with said source of caustic solution; a second tank influid communication with said source of a pH-raising agent, said sourceof CO₂ gas, and said first tank; and a filter in fluid communicationwith said second tank, wherein said filter is adapted to separate asecond scale-forming compound from the solution in said second tank 26.The system of claim 1, wherein the desalination system comprises aninlet, a preheater, a degasser, a plurality of evaporation chambers,demisters, heat pipes, and product condensers, a waste outlet, multipleproduct outlets, a heating chamber, and a control system, wherein theheat of condensation is recovered and reused for additional evaporation,such that water purified in the system has levels of all contaminanttypes below the levels shown in Table 1, when the contaminated water haslevels of the contaminant types that are up to 25, 50, 100, or 1,000times greater than the levels shown in Table
 1. 27. The system of claim26, wherein the volume of water produced is between about 20% and about99% of a volume of input water.
 28. The system of claim 26, wherein thesystem does not require cleaning through periods of use of at leastabout two months, one year, five years, or more.
 29. The system of claim26, further comprising an inlet switch to regulate flow of water throughthe inlet.
 30. The system of claim 29, wherein the switch comprises amechanism selected from the group consisting of: a solenoid, a valve,and an aperture.
 31. The system of claim 29, wherein the inlet switch iscontrolled by the control system.
 32. The system of claim 1, furthercomprising a shutdown control.
 33. The system of claim 32, wherein theshutdown control is selected from the group consisting of: a manualcontrol, a flood control, a condenser tank capacity control, and anevaporation chamber capacity control.
 34. The system of claim 32,wherein the control system controls the inlet based upon feedback fromat least one detection method selected from the group consisting of: atemperature sensor in a boiler, a condenser tank float, and a flooddetector.
 35. The system of claim 31, wherein the control systemcontrols the switch based upon feedback from the pre-treatment anddesalination system.
 36. The system of claim 1, further comprising aflow controller.
 37. The system of claim 36, wherein the flow controllercomprises a pressure regulator.
 38. The system of claim 37, wherein thepressure regulator maintains water pressure between about 0 kPa and 250kPa (0 to 36 psi).
 39. The system of claim 26, wherein water exiting thepreheating chamber has a temperature of at least about 96° C.
 40. Thesystem of claim 26, wherein the degasser is in a substantially verticalorientation, having an upper end and a lower end.
 41. The system ofclaim 40, wherein heated water from the preheating chamber enters thedegasser proximate to the upper end.
 42. The system of claim 40, whereinthe heated water exits the degasser proximate to the lower end.
 43. Thesystem of claim 26, wherein steam from the evaporation chamber entersthe degas ser proximate to the lower end.
 44. The system of claim 43,wherein the steam exits the degasser proximate to the upper end.
 45. Thesystem of claim 40, wherein the degasser comprises a matrix adapted tofacilitate the mixing of water and steam.
 46. The system of claim 45,wherein the matrix comprises substantially spherical particles.
 47. Thesystem of claim 45, wherein the matrix comprises non-sphericalparticles.
 48. The system of claim 45, wherein the matrix comprisesparticles having a size selected to permit uniform packing within thedegasser.
 49. The system of claim 45, wherein the matrix comprisesparticles of distinct sizes, wherein the particles are arranged in thedegasser in a size gradient.
 50. The system of claim 42, wherein waterexiting the degasser is substantially free of organics and volatilegasses.
 51. The system of claim 26, wherein the evaporation chambersinclude a plurality of heat pipes delivering heat that is transferredfrom lower condenser chambers.
 52. The system of claim 51, wherein theevaporation chamber further comprises a drain, and wherein the drain isat or about the middle of the chamber.
 53. The system of claim 26, theheating chamber further comprising electric heating elements, gas or oilburners, or heat pipes that transfer heat from waste heat sources, andwherein the heating chamber is adjacent to the bottom portion of theevaporation chamber.
 54. The system of claim 26, wherein the demister ispositioned proximate to an upper surface of the evaporation chamber. 55.The system of claim 26, wherein steam from the evaporation chamberenters the demister under pressure.
 56. The system of claim 26, whereinthe evaporation chamber prevents condensed droplets from entering thedemister by means of baffle guards and metal grooves.
 57. The system ofclaim 54, wherein the demister control parameter comprises at least oneparameter selected from the group consisting of: a recessed position ofa clean steam outlet, a pressure differential across the demister, aresistance to flow of a steam inlet, and a resistance to flow of a steamoutlet.
 58. The system of claim 26, further comprising heat pipes forcooling the condenser product.
 59. The system of claim 26, whereinproduct water exits the product condensers through the product outlets.60. The system of claim 26, wherein waste water exits the system throughthe waste outlet.
 61. A method of purifying and desalinating water,comprising the steps of: providing a source of inlet water comprising atleast one contaminant in a first concentration; modifying the pH of theinlet water to cause precipitation of insoluble hydroxides andseparating the precipitates from the incoming water; adding a source ofcarbonate ions and modifying the pH to cause precipitation of insolublecarbonates and separating the precipitates from the incoming water;passing the descaled pre-treated water through a preheating chambercapable of raising the temperature of the inlet water above 90° C.;removing essentially all organics, volatiles, and gasses from the inletwater by counterflowing the inlet water against an opposite directionalflow of a gas in a degasser; maintaining the water in an evaporationchamber for an average residence time of between 1 and 90 minutes orlonger under conditions that permit the formation of steam; dischargingsteam from the evaporation chamber to a demister; separating clean steamfrom contaminant-containing waste in the demister; condensing the cleansteam to yield purified water, comprising the at least one contaminantin a second concentration, wherein the second concentration is lowerthan the first concentration; recovering and transferring heat from acondenser chamber into an upper boiling or preheating chamber, such thatthe amount of heat recovered is at least 50%, 60%, 70%, 80%, 90%, ormore of the heat of condensation; repeating the evaporation,condensation, and demisting operations multiple times in order to re-usethe energy while maximizing clean water production.
 62. The method ofclaim 61, wherein the at least one contaminant is selected from thegroup consisting of: microorganisms, radionuclides, salts, organics, anddisinfection by-products, as listed in Table 3; and wherein the secondconcentration is not greater than the concentration shown in Table 3,and wherein the first concentration is at least about 10 times thesecond concentration.
 63. The method of claim 61, wherein the stackedarrangement of boilers, condensers, and preheater is enclosed in a metalshell, with perforated plates that separate the boiling and condenserchambers.
 64. The method of claim 61, wherein the perforated platesallow the passage of heat pipes, the degasser, demisters, brine overflowtubes, and waste stream tubes.
 65. The method of claim 61, wherein theboilers, preheaters, and heat pipes are constructed from non-corrosivematerials, such as titanium alloys or polymer-coated metals.